I am creating my customized Live CD based on CentOS 7.3. For this I use livecd-creator program and custom kickstart-file. This time I have a problem: RAM-disk, created by My livecd, uses maximum 4 GB of PC RAM.

But, in this case, I can't copy some files when I have free memory less than 500 MB of this 4 GB memory block.

I think, in this operations OS is limited by this 4GB memory block - although much more memory blocks may be availaible in RAM. OS detects all the memory in fact.